My earlier U.S. Pat. No. 3,954,264 discloses a bowling pin sweeper which is formed by a sweeper arm, moved longitudinally with respect to the bowling alley, to sweep fallen bowling pins into a pit from which they can be picked up by automatic pin removal apparatus. To provide a rapid drop of the bowling pin sweeper for removal of fallen bowling pins, without jamming of pins between the sweeper arm, an electromagnic release such as a magnet, operated as sear is triggered, for example, by movement of a bowling ball towards the pins, e.g. when the ball passes a lightgate, or other proximity sensing device. Upon having sensed that a ball has been thrown, and after it has passed the sweeper, the sear is triggered to release the sweeper arm to drop by its own weight prior to initiation of sweeping operation. The terminal portion of the drop can be braked by a dashpot. The sweeper arm, thus, will fall rapidly, and can then sweep the balls away at normal, sweeping speed. The system, thus, provides for two different speeds for different motions. A pin sweeper arm is guided on a essentially horizontal guide rails for reciprocating sweeping movement. The arm can be held in a raised position and lowered for subsequent movement along the guide rails upon initiation of the sweeping cycle. The arm is held by a holding hook which is pivotable about an essentially horizontal axis. A vertically removable frame is provided, normally located in raised position with respect to the rails. The frame is moveable to drop to a position in which the hook can engage the sweeper arm upon termination of the sweeping cycle of the sweeper arm, to raise the sweeper arm, preparatory for subsequent dropping upon the initiation of the next operating cycle. Electromagnetic means are provided connected to the means which hold the arm which, upon energization, are operable to rapidly release the arm to permit dropping thereof by gravity, thus rapidly lowering the arm. A two-part locking mechanism is provided; one of the parts is connected to the hook and is moveable therewith; the other one of the parts is operatively connected to the electromagnic means and operated thereby upon energization to unlock the second part, to permit release of the hook, and hence rapid dropping of the sweeper arm.
In actual practice it has been found that bowlers who are careless may throw a bowling ball shortly before the wiper arm has cleared the fallen pins off the bowling alley, and has not yet returned to its raised position. If, at this time, the engagement hook which is provided to raise the arm has already been engaged, and the sweeper arm is suddenly struck with the force of a bowling ball, damage to the lifting and dropping mechanism of the wiper may result.